“And in the case of Snowden, his revelations go to the core of what we are saying about the need for transparency, the need for consultation,” she said as she launched a report on the right to privacy in the digital age.

Pillay, a former judge at the International Criminal Court, declined to call on US President Barack Obama to pardon Snowden.

Pressed repeatedly on the issue, she said: “I’m not going to say whether he should be pardoned. He’s facing charges, and as a former judge I know that if he’s facing judicial proceedings, we should wait for that outcome.”

“I’m raising some very important arguments that could be raised on his behalf so that these criminal proceedings are averted,” she added.

“If he’s given a fair trial and all these points are raised about him, about the way people view his role, that would also be a good outcome,” the former South African high court judge said.

Snowden’s leaks last year sparked a massive row over the huge Internet and phone data sweeps conducted by US National Security Agency, including of allied nations and their leaders.

“We do owe it to him for drawing our attention to this issue,” Pillay said.

“I think that his revelations have also encouraged national authorities to be more accountable,” she added.

She said that when conducted legally, surveillance of electronic communications could be an effective and necessary measure for legitimate law enforcement or intelligence purposes.

The responsibility lies with states, however, to demonstrate the necessity of such surveillance and only to take measures that are proportionate and comply with clear legislation, she said.

When governments step beyond the limits, they must be exposed, she insisted.

“In these cases, the public interest in disclosure outweighs the public interest in non-disclosure. Such whistleblowers should be protected from legal reprisals and disciplinary action when disclosing unauthorised information,” she said.

Snowden fled to Russia after he leaked details of the secret state surveillance programmes, and Moscow is reportedly likely to extend his temporary asylum permit when it runs out at the end of July.